1. Field of the Invention
The present invention relates to printing apparatuses and printing methods.
2. Description of the Related Art
To date, image printing apparatuses are known which form an image on a print medium by ejecting ink to the print medium while moving a print head having a plurality of nozzles for ejecting ink arrayed therein relative to the print medium. In such image printing apparatuses, a so-called multipass method is employed through which a unit area of the print medium is scanned a plurality of times.
In such printing apparatuses, in a case in which the frequency at which ink is ejected is high, the following phenomenon is known to occur. Ink ejected through the nozzles drags in the air around the surface of the nozzles when moving toward the print medium, and thus the vicinity of the surface of a member in which the nozzles are formed (hereinafter, also referred to as a face) becomes depressurized. It is known that, in order to compensate for such a depressurized state, the air around the surface of the print medium moves toward the surface of the nozzles, and an air current is thus generated. Such an ascending air current toward the nozzles from the print medium tends to be greater as the amount of ink ejected at once is greater. A phenomenon in which an ink droplet generated as ejected ink splashes at the print medium or a so-called satellite ink droplet generated from a tail of ejected ink is dragged in by the ascending air current so as to travel in an opposite direction to adhere to the surface of the nozzles (hereinafter, referred to as face wetting) occurs. If ink is ejected through the nozzles after face wetting has occurred, the wet surface affects the ink at the time of ejecting the ink, and thus the ejection performance such as the direction in which the ink is ejected or the speed of the ejected ink varies. Therefore, the ink might not land on the print medium at a desired position.
Japanese Patent Laid-Open No. 1-71758 discloses a technique for suppressing a deterioration of printing quality due to face wetting, in which the number of dots formed in a unit area when the unit area is scanned by a print head is obtained and the surface of the nozzles is wiped on the basis of the obtained number of dots. According to the disclosed technique, the surface of the nozzles is wiped in a case in which the obtained number of dots exceeds a first value, and the surface of the nozzles is also wiped in a case in which a cumulative number of dots formed through scans spanning from a scan carried out immediately after the last time the surface is wiped to a scan to be carried out on a given unit area exceeds a second value.
However, according to the technique disclosed in Japanese Patent Laid-Open No. 1-71758, the face is wiped to remove the ink that has adhered to the face each time it is detected that face wetting has occurred at a notable level, and thus it takes a long time to completely form an image on the print medium. For example, in a case in which an image that is completely formed by ejecting ink on substantially the entire area of a single sheet of the print medium (hereinafter, referred to as a solid image) is to be printed, it is speculated that face wetting occurs fairly frequently, and thus an influence on the throughput of printing increases.